Since the discovery of ferrocene in 1951, a number of metallocenes have been prepared by the combination of compounds prepared from cyclopentadiene-type, indenyl type, and fluorenyl type compounds and various transition metals.
Many of such metallocenes have been found useful in catalyst systems for the polymerization of olefins. It has been noted in the art that variations in the chemical structure of such cyclopentadienyl-type metallocenes can have significant effects upon the suitability of the metallocene as a polymerization catalyst. For example, the size and location of substituents on cyclopentadienyl-type ligands has been found to affect the activity of the catalyst, the stereoselectivity of the catalyst, the stability of the catalyst, or various properties of the resulting polymer. However, the effects of various substituents is still largely an empirical matter; that is, experiments must be conducted in order to determine just what effect a particular variation in the chemical structure of the metallocene will have upon its behavior as a polymerization catalyst.
While there are many references in the prior art which contain broad general formulas that encompass a vast number of unbridged and bridged metallocenes, it is considered unlikely that all of the metallocenes within the broad disclosures of such publications have actually been prepared and evaluated for the polymerization effects.
In addition, many of the metallocenes have been found not to be sufficiently active in the polymerization of olefins to be of significant commercial interest. Prior to the present applicants' work, there does not appear to have been any work which either provides a N-bridged metallocene or suggests what effect a nitrogen bridge would have on a bridged cyclopentadienyl metallocene.
It is thus an object of the present invention to provide new Si--N--Si bridged metallocenes.
Another object of the present invention is to provide novel metallocene complexes which are useful for the production of Si--N--Si bridged metallocenes.
Still another object of the present invention is to provide a process for the production of Si--N--Si bridged metallocenes.
A still further object of this invention is to provide a novel catalyst system having as a component thereof a Si--N--Si bridged metallocene.
A still further object of this invention is to provide a process for the production of olefin polymers using a catalyst system wherein a component of same is a Si--N--Si bridged metallocene.
Other aspects, objects, and the several advantages of the present invention will be apparent in view of the following specification and claims.